1. Field of the Invention
The present general inventive concept relates to a hard disk drive, a method of controlling a flying height of a magnetic head of the hard disk drive, and a recording medium to contain computer-readable codes as a computer program to execute the method, and more particularly, to a hard disk drive which can maintain a target flying height of a magnetic head in a variety of environments, a method of controlling the flying height of a magnetic head of the hard disk drive, and a recording medium to contain computer-readable codes as a computer program to execute the method.
2. Description of the Related Art
Hard disk drives (HDDs) formed of electronic parts and mechanical parts are one of memory devices for recording and reproducing data by converting digital electric pulses to a magnetic field. The HDD is widely used as one of auxiliary memory devices for a computer system because of its fast access time to a large amount of data.
With the recent increase in TPI (tracks per inch) and BPI (bits per inch), the HDD has a high storage capacity and its application field has expanded. Accordingly, there have been active developments about compact HDDs which can be used for portable electronic products such as notebook computers, personal digital assistants (PDAs), and mobile phones. A compact HDD having a diameter of 2.5 inches are developed and already applied to notebook computers. Also, a compact HDD having a diameter of 0.85 inches, which is smaller than the 2.5 inch HDD, has been recently developed and is already used, or expected to be used in mobile phones or MP3 players.
As the storage capacity of the HDD increases, the size of a read/write sensor of a magnetic head decreases and a flying height (FH) of the magnetic head flying above a recording surface of a disk gradually decreases. That is, when high TPI and BPI are embodied to manufacture an HDD with a high storage capacity, the width of a track decreases and accordingly the strength of a magnetic field decreases in proportional thereto. Thus, when the FH of a magnetic head increases, the detection of a magnetic head is difficult so that the operation of the HDD is not smooth.
In this regard, a study on a method for effectively reducing the FH of a magnetic head with respect to a disk is actively performed. One of the methods is to reduce distribution of the FH of a magnetic head and the other method is to effectively reduce the FH of a magnetic head to obtain the minimum FH of a magnetic head.
Also, a study on a method for effectively reducing the FH of a magnetic head with respect to a disk by appropriately controlling the FH of the magnetic head is widely performed, and one of the methods is flying on demand (FOD). The FOD is a method for controlling the FH of a magnetic head using a reduction characteristic of the FH of a magnetic head generated during thermal expansion of a pole tip that is an end portion of the magnetic head, during the operation of the HDD, by applying a constant voltage, that is, an FOD voltage, to a heater coil included in the magnetic head.
Recently, a reference FOD voltage (or an FOD current or FOD power) profile indicating a relationship between the FH of a magnetic head and an FOD voltage is calculated using an FOD apparatus in a burn-in process. The FOD voltage is selected to maintain a desired FH of a magnetic head in a user's environment based on the reference FOD voltage profile. In detail, in the burn-in process, when a gradually increasing FOD voltage is applied to the magnetic head through a touch down test, the magnetic head maintaining a flying state at a predetermined height is gradually lowered toward the disk and finally touched down on the disk. The reference FOD voltage profile indicating the relationship between the FOD voltage and the FH of the magnetic head is provided through the touch down test.
A target clearance, that is, an FOD voltage needed for a target FH, in an actual user environment is calculated from the reference FOD voltage profile, and related data is stored in a maintenance cylinder of a disk. Thus, the FOD voltage calculated in the burn-in process is applied to the heater included in the magnetic head in the user environment so that a target FH of the magnetic head is maintained.
However, the environment where the HDD is actually in use is quite various and different from a reference environment so as not to be the same as that of the burn-in process. Accordingly, when the FOD voltage needed for a target FH that is selected based on the reference FOD voltage profile provided in the burn-in process is applied to the user environment where the HDD is in use, the FH of the magnetic head may vary according to the environment where the HDD is used. In particular, since a temperature sensor is generally included in the HDD, even when the effect by a temperature is compensated for to a degree by measuring a change in the temperature using the temperature sensor, it is very difficult to reflect a change in the altitude or humidity that affects the FH of the magnetic head.
When the HDD is used in the user environment based on the FOD voltage measured in the burn-in process, the target FH of the magnetic head may not be maintained due to an effect of a combination of various environment variables. When the target FH of the magnetic head is not maintained, a problem of weak write or head disk interference can be generated so that the reliability of FOD is deteriorated.
Also, in the method for controlling the FH of the magnetic head using the FOD voltage calculated based on the reference FOD voltage profile provided in the burn-in process, since the FOD voltage is not an actual value based on the actual FH of the magnetic head in the actual user environment but an estimated value approximated to the actual value, the FHs of the magnetic head operating in a variety of environments cannot be accurately controlled.